Integrated circuit device having an injection-locked oscillator

ABSTRACT

A variable injection-strength injection-locked oscillator (ILO) is described. The variable injection-strength ILO can output an output clock signal based on an input clock signal. The variable injection-strength ILO can pause, restart, slow down, or speed up the output clock signal synchronously with respect to the input clock signal in response to receiving power mode information. Specifically, the variable injection-strength ILO can be operated under relatively strong injection when the input clock signal is paused, restarted, slowed down, or sped up.

RELATED APPLICATION

This application is a continuation of, and claims priority to, U.S.application Ser. No. 13/988,615, having the same title and inventors asthe instant application, filed 21 May 2013, which is herein incorporatedby reference in its entirety for all purposes. U.S. application Ser. No.13/988,615 is a national stage application of, and claims priority to,International Application No. PCT/US 11/60215, having the same title andinventors as the instant application, filed 10 Nov. 2011, which isherein incorporated by reference in its entirety for all purposes.International Application No. PCT/US 11/60215 claims benefit of U.S.Provisional Application No. 61/419,459, having the same title andinventors as the instant application, filed 3 Dec. 2010, which is hereinincorporated by reference in its entirety for all purposes.

FIELD

This disclosure relates to electronic circuits. More specifically, thisdisclosure generally relates to an injection-locked oscillator (ILO),for example, in an integrated circuit device.

BACKGROUND Related Art

The mobile computing revolution has enhanced the efficiency in howpeople communicate and interact with one another. Mobile devices areusually designed to meet stringent power constraints so that they canoperate on batteries for a reasonably long time. To reduce powerconsumption, mobile devices may use circuits that have multiple powermodes. Specifically, a mobile device may need to transition a circuitrapidly from one power mode to another power mode.

Some circuits may not be suitable for use in devices that have multiplepower modes, especially if the circuits need to be transitioned rapidlyfrom one power mode to another power mode. Further, in some circuits,latency may be incurred when recovering from power down modes.Specifically, powering up an ILO can create unpredictable transients inthe ILO's output clock signal. Furthermore, latching and unlatching theILO's output clock signal synchronously with respect to the input clocksignal is not practical at high clock frequencies.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a variable injection-strength injection-lockedoscillator in accordance with some embodiments described in thisdisclosure.

FIGS. 2A-2C illustrate signal waveforms associated with a variableinjection-strength ILO operating in a weak-injection-strength mode inaccordance with some embodiments described in this disclosure.

FIGS. 3A-3C illustrate signal waveforms associated with a variableinjection-strength ILO operating in a strong-injection-strength mode inaccordance with some embodiments described in this disclosure.

FIG. 4 illustrates a variable injection-strength ILO in accordance withsome embodiments described in this disclosure.

FIG. 5 illustrates a variable injection-strength ILO in accordance withsome embodiments described in this disclosure.

FIG. 6 illustrates a variable injection-strength ILO in accordance withsome embodiments described in this disclosure.

FIG. 7A illustrates a variable injection-strength ILO that is capable ofbeing powered down during a power saving mode in accordance with someembodiments described in this disclosure.

FIG. 7B illustrates waveforms associated with a variableinjection-strength ILO that is capable of being powered down during apower saving mode in accordance with some embodiments described in thisdisclosure.

FIG. 8 illustrates a variable injection-strength ILO that includes atank circuit (i.e., an oscillator based on an inductance/capacitancepair) in accordance with some embodiments described in this disclosure.

FIG. 9 illustrates a variable injection-strength ILO that includes aring oscillator in accordance with some embodiments described in thisdisclosure.

FIG. 10 presents a flowchart that illustrates a process for operating avariable injection-strength ILO in accordance with some embodimentsdescribed in this disclosure.

FIG. 11 illustrates a memory controller that includes a variableinjection-strength ILO in accordance with some embodiments described inthis disclosure.

DETAILED DESCRIPTION

Embodiments presented in this disclosure are directed to methods andapparatuses featuring an injection-locked oscillator (ILO) whoseinjection strength can be varied based on power mode information. Inthis disclosure, unless otherwise stated, the phrase “based on” means“based solely or partly on.”

FIG. 1 illustrates a variable injection-strength ILO in accordance withsome embodiments described in this disclosure. Variableinjection-strength ILO 102 outputs output clock signal 104 based oninput clock signal 106. In general, the methods and apparatusesdescribed in this disclosure are applicable to any system that uses oneor more ILOs.

An integrated circuit device, or circuits contained in such a device,can have multiple power modes. In some embodiments described in thisdisclosure, the integrated circuit device, or the circuits contained inthe device, can transition rapidly from one power mode to another powermode. In a normal power mode, one or more parts of a circuit may beclocked using a clock signal that is operating at a normal clockfrequency. In a power saving mode, the clock signal may be paused and/orthe frequency of the clock signal may be substantially reduced in one ormore parts of the circuit to reduce the dynamic power consumption of thecircuit. Note that a circuit can have multiple power saving modes, e.g.,different power saving modes of a circuit may slow down and/or pause theclock in different parts of the circuit.

Whenever a circuit transitions from one power mode to another, clocksignals may need to be paused, slowed down, restarted, and/or sped up.In some embodiments, a circuit may be calibrated at system startup sothat the data signal is sampled in the middle of the data eye. Tooperate correctly, the circuit may require the clock signal to becleanly paused and restarted. Some embodiments provide a fastturn-on/turn-off apparatus that can be used to cleanly pause, restart,slow down, or speed up the clock signal.

According to one definition, when a clock signal is cleanly paused,restarted, slowed down, or sped up, the clock signal does not causeunpredictable changes to the circuit state. According to anotherdefinition, an output clock signal of an ILO is cleanly paused,restarted, slowed down, or sped up if the output clock signalsynchronously tracks the input clock signal as the input clock signal ispaused, restarted, slowed down, or sped up. According to one definition,an output clock signal synchronously tracks an input clock signal ifeach transition in the input clock signal corresponds to exactly onewell-defined transition in the output clock signal. Note that thesedefinitions are neither exhaustive nor mutually exclusive.

In an embodiment, the ILO can be based on a tank circuit (i.e., aninductor/capacitor oscillator) or a ring oscillator, with one or morenodes for receiving an input clock signal, and one or more nodes foroutputting an output clock signal. In some embodiments, injectionlocking or injection pulling may occur when the oscillator is perturbedby an input clock signal whose frequency is relatively close to theoscillator's fundamental frequency, or relatively close to asub-harmonic or a super-harmonic of the oscillator's fundamentalfrequency.

The behavior of an ILO, in embodiments described herein, may depend onthe injection strength. If the injection strength is relatively weak,the oscillator runs relatively autonomously except that the oscillator'sfrequency and steady-state phase are dictated by the input clock signalonce the ILO locks onto the input clock signal. In some embodimentsdescribed herein, ILOs are operated under relatively weak injection toremove clock jitter, to de-skew clock signals, and/or to generate clocksignals.

In some embodiments, the ILO is operated under relatively stronginjection so that the injection signal overcomes the natural oscillationof the ILO. When an ILO is operated under relatively strong injection byan embodiment, the ILO's output clock signal can pause, restart, slowdown, and speed up synchronously with respect to the input clock signalwhen the input clock signal is paused, restarted, slowed down, and spedup, respectively. An embodiment may not operate the ILO under relativelystrong injection when the benefits of operating the ILO under relativelyweak injection are needed.

In some embodiments, when the circuit transitions from one power mode toanother, variable injection-strength ILO 102 can be operated underrelatively strong injection so that the output clock signal can besynchronously paused, restarted, slowed down, and/or sped up withrespect to the input clock signal. Once the circuit has transitioned tothe new power mode, the ILO may be operated under relatively weakinjection. In some embodiments, the performance requirements may be suchthat the benefits of operating the ILO under relatively weak injectionare not needed. In these embodiments, the ILO may continue to beoperated under relatively strong injection even after the transition tothe new power mode has been completed.

Specifically, variable injection-strength ILO 102 can receive power modeinformation 108, which may indicate that the circuit is transitioningfrom one power mode to another. For example, variable injection-strengthILO 102 may receive power mode information 108 that indicates that acircuit is about to enter a power saving mode. In response, variableinjection-strength ILO 102 may increase the injection strength so thatvariable injection-strength ILO 102 operates under relatively stronginjection. When variable injection-strength ILO 102 is operating underrelatively strong injection, input clock signal 106 may pause or theclock frequency of input clock signal 106 may reduce substantially(e.g., halve). If input clock signal 106 pauses, output clock signal 104may pause synchronously with respect to input clock signal 106. If theclock frequency of input clock signal 106 reduces substantially (e.g.,halves), output clock signal 104 may synchronously track input clocksignal 106, so that the clock frequency of output clock signal 104 alsoreduces accordingly.

Subsequently, input clock signal 106 may restart or the clock frequencyof input clock signal 106 may increase substantially (e.g., double). Ifinput clock signal 106 restarts, output clock signal 104 may restartsynchronously with respect to input clock signal 106. If the clockfrequency of input clock signal 106 increases substantially (e.g.,doubles), output clock signal 104 may synchronously track input clocksignal 106, so that the clock frequency of output clock signal 104 alsoincreases accordingly. Variable injection-strength ILO 102 may thenreceive power mode information 108 that indicates that the circuit hascompleted transitioning to a power mode, e.g., a normal power mode. Inresponse, variable injection-strength ILO 102 may decrease the injectionstrength so that the ILO operates under relatively weak injection.

In some embodiments, the ILO locks onto the input clock signal over arange of frequency values, called the ILO's locking range. In theseembodiments, the locking range can be defined as the frequency rangeover which the output clock signal of the ILO synchronously tracks theinput clock signal. According to one definition, the output clock signalsynchronously tracks the input clock signal if the frequency of theoutput clock signal tracks the frequency of the input clock signal. Inthese embodiments, the phase delay between the output clock signal andthe input clock signal may change when the frequency of the input clocksignal is changed.

Increasing the injection strength can be viewed as increasing thelocking range of variable injection-strength ILO 102. Conversely,decreasing the injection strength can be viewed as decreasing thelocking range of variable injection-strength ILO 102.

Variable injection-strength ILO 102 can be viewed as having multipleoperating modes, each with a different locking range. For example,variable injection-strength ILO 102 can have a first operating mode,e.g., a normal-locking-range mode, and a second operating mode, e.g., alarge-locking-range mode. In the normal-locking-range mode, output clocksignal 104 synchronously tracks input clock signal 106 over a normalfrequency range, and in the large-locking-range mode, output clocksignal 104 synchronously tracks input clock signal 106 over a largefrequency range, which is greater than the normal frequency range.

The injection strength in the large-locking-range mode is greater thanthe injection strength in the normal-locking-range mode. Variableinjection-strength ILO 102 can be operated in the normal-locking-rangemode when the circuit is operating in a normal power mode. Variableinjection-strength ILO 102 can be operated in the large-locking-rangemode when the circuit transitions from one power mode to another, e.g.,before the input clock signal is paused or slowed down in a power savingmode.

FIGS. 2A-2C illustrate signal waveforms associated with a variableinjection-strength ILO operating in a weak-injection-strength mode inaccordance with some embodiments described in this disclosure. Thesignal waveforms shown in FIGS. 2A-2C are for illustration purposesonly. Input clock waveforms 202, 206, and 210 can correspond to inputclock signal 106. Output clock waveforms 204, 208, and 212 cancorrespond to output clock signal 104. Output clock waveforms 204, 208,and 212 can have a phase delay with respect to input clock waveforms202, 206, and 210, respectively. However, phase delays have not beenshown in FIGS. 2A-2C for the sake of clarity and ease of discourse.

In a weak-injection-strength mode, a variable injection-strength ILO cansubstantially reduce jitter from the input clock signal. For example, asshown in FIG. 2A, the jitter in input clock waveform 202 has beenremoved in output clock waveform 204.

In a weak-injection-strength mode, if the input clock signal is paused,a variable injection-strength ILO may continue outputting an outputclock signal whose frequency is approximately equal to the ILO'sfree-running frequency. For example, as shown in FIG. 2B, output clockwaveform 208 toggles at the ILO's free-running frequency even when inputclock waveform 206 is paused.

In a weak-injection-strength mode, a variable injection-strength ILO maynot lock on the input clock signal if the frequency of the input clocksignal is changed substantially. If the ILO does not lock on the inputclock signal, it may output a clock signal whose frequency is equal tothe ILO's free-running frequency. As shown in FIG. 2C, when thefrequency of input clock waveform 210 changes from f to f/2, outputclock waveform 212 may continue to output a clock signal at frequency f,although perhaps at a different phase (not shown in FIG. 2C).

FIGS. 3A-3C illustrate signal waveforms associated with a variableinjection-strength ILO operating in a strong-injection-strength mode inaccordance with some embodiments described in this disclosure. Thesignal waveforms shown in FIGS. 3A-3C are for illustration purposesonly. Input clock waveforms 302, 306, and 310 can correspond to inputclock signal 106. Output clock waveforms 304, 308, and 312 cancorrespond to output clock signal 104. Output clock waveforms 304, 308,and 312 can have a phase delay with respect to input clock waveforms302, 306, and 310, respectively. However, phase delays have not beenshown in FIGS. 3A-3C for the sake of clarity and ease of discourse.

In comparison to a weak-injection-strength mode, a variableinjection-strength ILO operating in a strong-injection-strength mode maynot be able to reduce as much jitter from the input clock signal over aswide a range of jitter frequencies. In other words, the variableinjection-strength ILO may pass more high frequency jitter from theinput clock waveform to the output clock waveform in astrong-injection-strength mode than in a weak-injection-strength mode.For example, as shown in FIG. 3A, the jitter in input clock waveform 302has been reduced by a much lesser extent in output clock waveform 304.

In a strong-injection-strength mode, if the input clock signal pauses, avariable injection-strength ILO can pause the output clock signalsynchronously with respect to the input clock signal. For example, asshown in FIG. 3B, output clock waveform 308 pauses synchronously withrespect to input clock waveform 306.

In a strong-injection-strength mode, a variable injection-strength ILOmay synchronously track the input clock signal even if the frequency ofthe input clock signal is changed substantially. For example, as shownin FIG. 3C, output clock waveform 312 synchronously tracks input clockwaveform 310 as it changes its frequency from f to f/2.

FIG. 4 illustrates a variable injection-strength ILO in accordance withsome embodiments described in this disclosure. Variableinjection-strength ILO 402 is capable of varying the injection strengthin response to receiving power mode information 408. Variableinjection-strength ILO 402 can include amplifier 412, injection-strengthcontroller 414, and ILO 410. Input clock signal 406 can be amplified byamplifier 412 to produce adjusted input clock signal 418. Adjusted inputclock signal 418 can be provided as input to ILO 410, which can produceoutput clock signal 404. ILO 410 may receive free-run frequency controlsignal 416, which can be used to control the free-running frequency ofan oscillator within ILO 410.

The gain of amplifier 412 can be controlled by injection-strengthcontroller 414. Injection-strength controller 414 can increase the gainof amplifier 412 to operate ILO 410 under relatively strong injection,and decrease the gain of amplifier 412 to operate ILO 410 underrelatively weak injection. For example, variable injection-strength ILO402 may receive power mode information 408 that indicates that a circuitis about to transition between two power modes, e.g., from a normalpower mode to a power saving mode. In response, injection-strengthcontroller 414 may increase the gain of amplifier 412 so that ILO 410operates under relatively strong injection. Subsequently, variableinjection-strength ILO 402 may receive power mode information 408 thatindicates that a circuit has completed transitioning to a power mode,e.g., a normal power mode. In response, injection-strength controller414 may decrease the gain of amplifier 412 so that ILO 410 operatesunder relatively weak injection.

FIG. 5 illustrates a variable injection-strength ILO in accordance withsome embodiments described in this disclosure. Variableinjection-strength ILO 502 is capable of varying the injection strengthin response to receiving power mode information 508. Variableinjection-strength ILO 502 can include injection-strength controller 514and ILO 510. Input clock signal 506 can be provided as input to ILO 510,which can produce output clock signal 504.

ILO 510 may receive free-run frequency control signal 516, which can beused to control the free-running frequency of an oscillation signalwithin ILO 510. The oscillation signal within ILO 510 can be perturbedbased on input clock signal 506. The output from injection-strengthcontroller 514 can be used to control the amplitude of the oscillationsignal within ILO 510. Injection-strength controller 514 can decreasethe amplitude of the oscillation signal within ILO 510 to operate ILO510 under relatively strong injection, and increase the amplitude of theoscillation signal within ILO 510 to operate ILO 510 under relativelyweak injection.

FIG. 6 illustrates a variable injection-strength ILO in accordance withsome embodiments described in this disclosure. Variableinjection-strength ILO 602 is capable of varying the injection strengthin response to receiving power mode information 608. Variableinjection-strength ILO 602 can include injection-strength controller 614and ILO 610. Input clock signal 606 can be provided as input toinjection clock signal generator 618, which may output multiple copiesof input clock signal 606 which may or may not have different phasedelays. The multiple outputs from injection clock signal generator 618may be provided as inputs at multiple injection points in ILO 610, whichcan produce output clock signal 604.

ILO 610 may receive free-run frequency control signal 616, which can beused to control the free-running frequency of an oscillation signalwithin

ILO 610. The output from injection-strength controller 614 can be usedto control the number of injection points in ILO 610 that are injectedwith an injection clock signal. Injection-strength controller 614 canincrease the number of injection points to operate ILO 610 underrelatively strong injection, and decrease the number of injection pointsto operate ILO 610 under relatively weak injection.

FIG. 7A illustrates a variable injection-strength ILO that is capable ofbeing powered down during a power saving mode in accordance with someembodiments described in this disclosure. Variable injection-strengthILO 702 outputs output clock signal 704 based on input clock signal 706.Variable injection-strength ILO 702 can receive power mode information708 and power down/up information 710 (e.g., an enable/disable signal).

Latch 712 receives output clock signal 704 and produces latch output714. When latch 712 is unlatched, it passes the input signal to itsoutput, i.e., latch output 714 toggles synchronously with output clocksignal 704. When latch 712 is latched, latch output 714 outputs thelatched signal value. Latch 712 can be latched and unlatched based onpower down/up information 710. When input clock signal 706 is toggling(e.g., in a normal power mode or a slow down mode), latch 712 is keptunlatched. Latch 712 may be latched after input clock signal 706 hasbeen paused.

FIG. 7B illustrates waveforms associated with the system shown in FIG.7A in accordance with some embodiments described in this disclosure. Thewaveforms shown in FIG. 7B are for illustration purposes only. As shownin FIG. 7B, variable injection-strength ILO 702 may receive power modeinformation 708 that indicates that a circuit is about to transitionbetween two power modes, e.g., from a normal power mode to a powersaving mode. In response, variable injection-strength ILO 702 mayincrease the injection strength so that the ILO operates underrelatively strong injection. After power mode information 708 isreceived by variable injection-strength ILO 702, input clock signal 706may pause. Since variable injection-strength ILO 702 is operating underrelatively strong injection, output clock signal 704 pausessynchronously with respect to input clock signal 706. Next, powerdown/up information 710 may indicate that variable injection-strengthILO 702 is to be powered down. In response, the signal value of outputclock signal 704 may be latched by latch 712, and then variableinjection-strength ILO 702 may be powered down.

Subsequently, power down/up information 710 may indicate that variableinjection-strength ILO 702 is to be powered up. In response, variableinjection-strength ILO 702 may be powered up, and then latch 712 may beunlatched after the output of variable injection-strength ILO 702 hasstabilized.

Next, input clock signal 706 may restart. Since variableinjection-strength ILO 702 is operating under relatively stronginjection, it restarts output clock signal 704 synchronously withrespect to input clock signal 706. Further, since latch 712 isunlatched, latch output 714 outputs the output clock signal 704, whichwas restarted synchronously with respect to input clock signal 706.Variable injection-strength ILO 702 may then receive power modeinformation 708 that indicates that the circuit has entered a normalpower mode. In response, variable injection-strength ILO 702 maydecrease the injection strength so that the ILO operates under weakinjection.

FIG. 8 illustrates a variable injection-strength ILO that includes atank circuit (i.e., an oscillator based on an inductance/capacitancepair) in accordance with some embodiments described in this disclosure.Signals S_(INJ) and S _(INJ) correspond to the injection clock signal,signals S_(OUT) and S _(OUT) correspond to the output clock signal, andV_(DD) is the supply voltage. The amplitude of the ILO's oscillationsignal can be changed by using bias signal S_(BIAS). Specifically, theILO can be operated under relatively strong injection by eitherincreasing S_(BIAS,INJ) (which, in turn, increases the amplitude of theinjection clock signal) or by decreasing S_(BIAS) (which, in turn,decreases the amplitude of the oscillator's signal). Conversely, the ILOcan be operated under relatively weak injection by either decreasingS_(BIAS,INJ) (which, in turn, decreases the amplitude of the injectionclock signal) or by increasing S_(BIAS) (which, in turn, increases theamplitude of the oscillator's signal). The free-running frequency of theLC oscillator can be changed by using the variable capacitor.

FIG. 9 illustrates a variable injection-strength ILO that includes aninverter based ring oscillator in accordance with some embodimentsdescribed in this disclosure. Signal S_(OUT) can correspond to theoutput clock signal and signals S_(INJ,1) and S_(INJ,S2) can correspondto the injection clock signals that are injected at two differentinjection points. Note that the injection clock signals that areinjected at the two injection points may have different phases. The ILOcan be operated under relatively strong injection by injecting theinjection clock signal at both injection points. The ILO can be operatedunder relatively weak injection by injecting the injection clock signalat only one of the two injection points. The ILO can be operated underrelatively strong injection by injecting the injection clock signal atone or both injection points with a relatively low impedance (or highcurrent) compared to the inverter device impedances (or currents). TheILO can be operated under relatively weak injection by injecting theinjection clock signal at one or both injection points with a relativelyhigh impedance (or low current) compared to the inverter deviceimpedances (or currents). The ILO can be operated under relativelystrong injection by increasing the impedance (or decreasing the drivecurrent) of the inverters relative to the impedance (or drive current)of the injection signals. The ILO inverters can be tri-state inverterswhich have a high output impedance state, and the inverters can beconfigured into the high output impedance state to operate the ILO underrelatively strong injection or into the normal impedance state tooperate the ILO under relatively weak injection.

FIG. 10 presents a flowchart that illustrates a process for operating avariable injection-strength ILO in accordance with some embodimentsdescribed in this disclosure. A variable injection-strength ILO mayreceive power mode information (operation 1002). In response toreceiving the power mode information, the variable injection-strengthILO can change the injection strength. Specifically, the variableinjection-strength ILO can increase injection strength if the power modeinformation indicates that a circuit is about to transition between twopower modes (operation 1004). The variable injection-strength ILO canoptionally decrease injection strength if the power mode informationindicates that a circuit has completed transitioning to a power mode(operation 1006). Specifically, if the performance requirements are suchthat the benefits of operating the ILO under relatively weak injectionare not needed, then the ILO may continue to be operated underrelatively strong injection even after the transition to the power modehas been completed.

FIG. 11 illustrates a memory controller that includes a variableinjection-strength ILO in accordance with some embodiments described inthis disclosure.

Memory controller 1100 may be coupled with memory module 1104 via one ormore signal lines, which may carry control signals, clock signals,and/or data signals. Memory controller 1100 may receive power modeinformation 1108, and include one or more ILOs, such as, variableinjection-strength ILO 1102. In some embodiments, memory controller 1100may use variable injection-strength ILO 1102 to remove clock jitter, tode-skew clock signals, and/or to generate clock signals. In someembodiments, memory controller 1100 may change the injection strength ofvariable injection strength ILO 1102 based on power mode information1108.

Any data structures and/or code described in this disclosure can bestored on a computer-readable storage medium, which may be any device ormedium that can store code and/or data for use by a computer system. Thecomputer-readable storage medium includes, but is not limited to,volatile memory, non-volatile memory, magnetic and optical storagedevices such as disk drives, magnetic tape, CDs (compact discs), DVDs(digital versatile discs or digital video discs), or other media capableof storing computer-readable media now known or later developed.

The methods and/or processes described in this disclosure can beembodied as code and/or data, which can be stored in a computer-readablestorage medium as described above. When a computer system reads andexecutes the code and/or data stored on the computer-readable storagemedium, the computer system performs the methods and/or processes.

Furthermore, the methods and/or processes described in this disclosurecan be embodied in hardware. Hardware embodiments include, but are notlimited to, application-specific integrated circuit (ASIC) chips,field-programmable gate arrays (FPGAs), and other programmable-logicdevices now known or later developed.

Various modifications to the disclosed embodiments will be readilyapparent to those skilled in the art, and the general principles definedherein may be applied to other embodiments and applications withoutdeparting from the spirit and scope of the present disclosure. Thus, thescope of the present disclosure is not limited to the embodiments shown,but is to be accorded the widest scope consistent with the principlesand features disclosed herein.

What is claimed is:
 1. A circuit, comprising: an input to receive aninput clock signal; an output to output an output clock signal; and avariable injection-strength injection-locked oscillator (ILO), whereinthe variable injection-strength ILO generates the output clock signalbased on the input clock signal and power mode information, and whereinthe output clock signal pauses synchronously with respect to the inputclock signal when the input clock signal pauses.
 2. The circuit of claim1, wherein the variable injection-strength ILO operates in one ofmultiple operating modes based on the power mode information; wherein,in a first operating mode, the output clock signal is not capable ofpausing synchronously with respect to the input clock signal when theinput clock signal pauses; and wherein, in a second operating mode, theoutput clock signal is capable of pausing synchronously with respect tothe input clock signal when the input clock signal pauses.
 3. Thecircuit of claim 2, wherein the variable injection-strength ILOgenerates an adjusted input signal based on the input signal, whereinthe adjusted input signal is used as an injection signal in the variableinjection-strength ILO, and wherein the amplitude of the adjusted inputclock signal in the second operating mode is greater than the amplitudeof the adjusted input clock signal in the first operating mode.
 4. Thecircuit of claim 2, wherein an oscillation signal within the variableinjection-strength ILO is perturbed based on the input clock signal, andwherein the amplitude of the oscillation signal in the second operatingmode is less than the amplitude of the oscillation signal in the firstoperating mode.
 5. The circuit of claim 2, wherein the input clocksignal is injected at multiple injection points in the variableinjection-strength ILO, and wherein the number of injection points inthe second operating mode is greater than the number of injection pointsin the first operating mode.
 6. The circuit of claim 2, furthercomprising control circuitry to operate the variable injection-strengthILO in the second operating mode or the first operating mode based onthe power mode information.
 7. The circuit of claim 6, wherein thecontrol circuitry operates the variable injection-strength ILO in thesecond operating mode if the power mode information indicates that thecircuit is about to transition between two power modes.
 8. The circuitof claim 6, wherein the control circuitry operates the variableinjection-strength ILO in the first operating mode if the power modeinformation indicates that the circuit has completed transitioning to apower mode.
 9. The circuit of claim 6, wherein the control circuitrylatches the output clock signal and powers down the variableinjection-strength ILO after the output clock signal pausessynchronously with respect to the input clock signal.
 10. The circuit ofclaim 9, wherein the circuitry powers up the variable injection-strengthILO and unlatches the output clock signal before the input clock signalis restarted.
 11. A circuit, comprising: an input to receive an inputclock signal; an output to output an output clock signal; and a variableinjection-strength injection-locked oscillator (ILO), wherein thevariable injection-strength ILO generates the output clock signal basedon the input clock signal, wherein the variable injection-strength ILOhas multiple operating modes including a first operating mode and asecond operating mode, wherein the locking range of the variableinjection-strength ILO in the first operating mode is less than thelocking range of the variable injection-strength ILO in the secondoperating mode, and wherein the variable injection-strength ILO isoperated in one of the multiple operating modes based on power modeinformation.
 12. The circuit of claim 11, further comprising controlcircuitry to operate the variable injection-strength ILO in one of themultiple operating modes, wherein the control circuitry operates thevariable injection-strength ILO in the second operating mode if thepower mode information indicates that the circuit is about to transitionbetween two power modes.
 13. The circuit of claim 12, wherein thecontrol circuitry operates the variable injection-strength ILO in thefirst operating mode if the power mode information indicates that thecircuit has completed transitioning to a power mode.
 14. The circuit ofclaim 11, wherein the variable injection-strength ILO generates anadjusted input clock signal based on the input clock signal, wherein theadjusted input clock signal is used as an injection clock signal in thevariable injection-strength ILO, and wherein the amplitude of theadjusted input clock signal in the second operating mode is greater thanthe amplitude of the adjusted input clock signal in the first operatingmode.
 15. The circuit of claim 11, wherein an oscillation signal withinthe variable injection-strength ILO is perturbed based on the inputclock signal, and wherein the amplitude of the oscillation signal in thesecond operating mode is less than the amplitude of the oscillationsignal in the first operating mode.
 16. The circuit of claim 11, whereinthe input clock signal is injected at multiple injection points in thevariable injection-strength ILO, and wherein the number of injectionpoints in the second operating mode is greater than the number ofinjection points in the first operating mode.
 17. A circuit, comprising:an input to receive an input clock signal; an output to output an outputclock signal; and a variable injection-strength injection-lockedoscillator (ILO), wherein the variable injection-strength ILO generatesan output clock signal based on an input clock signal, wherein thevariable injection-strength ILO is operated in one of multiple operatingmodes based on power mode information, wherein the multiple operatingmodes include a first operating mode and a second operating mode;wherein, in the first operating mode, the variable injection-strengthILO is capable of synchronously tracking the input clock signal over afirst frequency range; and wherein, in the second operating mode, thevariable injection-strength ILO is capable of synchronously tracking theinput clock signal over a second frequency range, wherein the secondfrequency range is greater than the first frequency range.
 18. Thecircuit of claim 17, further comprising control circuitry to operate thevariable injection-strength ILO in one of the multiple operating modes,wherein the control circuitry operates the variable injection-strengthILO in the second operating mode if the power mode information indicatesthat the circuit is transitioning between two power modes.
 19. Thecircuit of claim 18, wherein the control circuitry operates the variableinjection-strength ILO in the first operating mode if the power modeinformation indicates that the circuit has completed transitioning to apower mode.
 20. The circuit of claim 17, wherein the variableinjection-strength ILO generates an adjusted input clock signal based onthe input clock signal, wherein the adjusted input clock signal is usedas an injection signal in the variable injection-strength ILO, andwherein the amplitude of the adjusted input clock signal in the secondoperating mode is greater than the amplitude of the adjusted input clocksignal in the first operating mode. 21-29. (canceled)